Process for electroplating an aqueous adhesive composition comprising a phosphate salt and a thermosetting resin on a conductive element

ABSTRACT

The present invention relates to a process for electroplating an adhesive composition onto at least one conductive element, in which the conductive element is placed in contact with the adhesive composition comprising: a phosphate salt and a resin based on: a compound A1, compound A1 being chosen from a compound A11 comprising at least two functions, one of these functions being a hydroxymethyl function and the other being an aldehyde function or a hydroxymethyl function, or a compound A12 comprising at least one aldehyde function, or a mixture of a compound A11 and of a compound A12; and a phenol A21. A potential difference is applied between the conductive element and the adhesive composition to coat the conductive element with an adhesive layer.

The field of the present invention is that of conductive elements and adhesive compositions or “glues” intended to make such conductive elements adhere to elastomeric matrices, such as those commonly used in semi-finished elastomer articles or products, or else in the field of tyres or belts.

The present invention more particularly relates to a process for electroplating an adhesive composition onto at least one conductive element, to a device for electroplating an adhesive composition onto at least one conductive element, to a coated conductive element which may be obtained via the electroplating process, to the elastomeric composite comprising this conductive element and to tyres or belts reinforced with such elastomeric composites.

Steel wire elements for tyres comprising one or more steel wires are known in the prior art.

A first solution for making these steel wires adhere to elastomeric matrices is to use adhesives known under the name “RFL” (for resorcinol-formaldehyde latex), as described, for instance, in EP 2 006 341. These RFL adhesives comprise, in a well-known manner, a thermosetting phenolic resin, obtained by the condensation of resorcinol with formaldehyde, and one or more diene elastomeric latices in aqueous solution.

The RFL adhesives of EP 2 006 341 ensure good adhesion of the coated steel wire(s) to elastomeric matrices without these wires being surface-treated, that is to say in the absence of a layer of a metal coating, for example a layer of brass. However, the RFL adhesive requires the use of a halogenated polymer and of a metal oxide. In addition, this RFL adhesive requires the use of an elastomeric matrix comprising an acrylic rubber composition and thus does not allow satisfactory adhesion with just any elastomeric matrix.

A second solution for making these steel wires adhere to elastomeric matrices is to coat the steel wires with a layer of brass. This second solution is the most widespread and the most effective industrial solution. During the curing of the tyre, an adhesive interface is formed which comprises zinc oxide, zinc sulfide and copper sulfide resulting from the reaction between the brass and the elastomeric matrix. Such an interface and the corresponding physicochemical mechanisms are notably described in the article “Mechanism and theories of rubber adhesion to steel cords—An overview”, W. J. Van Ooij, Rubber Chemistry and Technology, 421-456, Vol. 57.

However, it is necessary, notably for the formation of copper sulfide and zinc sulfide, to have available an elastomeric matrix based on an elastomeric composition comprising a crosslinking system comprising a high content of molecular sulfur of between 6 and 12 phr. However, such an elastomeric matrix has, due to the high content of molecular sulfur, a limited shelf life because of the risks of pre-vulcanization of the elastomeric composition at room temperature.

Thus, the designers of elastomeric articles, notably tyre manufacturers, have the objective today of finding novel simple adhesive processes which make it possible to make conductive wire elements adhere satisfactorily to elastomeric matrices, without the latter necessarily being based on an acrylic rubber composition or without having to use the adhesive in combination with a halogenated polymer and a metal oxide.

It is desirable for this adhesion to be initially, i.e. after cooling following the curing, relatively high and for this adhesion to be sparingly degraded by corrosion.

In the course of its research, the Applicant has discovered a process which makes it possible to meet the above objective.

One subject of the invention is thus a process for electroplating an adhesive composition onto at least one conductive element, in which process:

-   -   the conductive element is placed in contact with the adhesive         composition comprising:         -   at least one phosphate salt and         -   at least one resin based on:             -   at least one compound A1, compound A1 being chosen from:                 -   a compound A11 comprising at least two functions,                     one of these functions being a hydroxymethyl                     function and the other being an aldehyde function or                     a hydroxymethyl function, or                 -   a compound A12 comprising at least one aldehyde                     function, or                 -   a mixture of a compound A11 and of a compound A12,                     and             -   at least one phenol A21,     -   a potential difference is applied between the conductive element         and the adhesive composition so as to coat the conductive         element with an adhesive layer based on the adhesive         composition.

The Applicant is thus putting forward the hypothesis that the electroplating process using the combination of the phosphate salt and of the resin makes it possible to create a passivation layer on the surface of the conductive element, this passivation layer firstly ensuring good initial adhesion between the conductive element and an elastomeric matrix and secondly ensuring high corrosion resistance of the adhesive interface, and doing so without, however, using a matrix of specific elastomer, of halogenated polymer and of metal oxide.

In addition, a better degree of coverage of the conductive element by the adhesive layer is obtained when compared with a conventional dip-coating process.

Furthermore, in addition to participating in the formation of the passivation layer, the phosphate salt has a buffer effect and makes it possible to stabilize the pH of the adhesive composition.

Another subject of the invention relates to a device for electroplating an adhesive composition onto at least one conductive element, the device comprising:

-   -   means for placing the conductive element in contact with an         adhesive composition, the adhesive composition comprising:         -   at least one phosphate salt and         -   at least one resin based on:             -   at least one compound A1, compound A1 being chosen from:                 -   a compound A11 comprising at least two functions,                     one of these functions being a hydroxymethyl                     function and the other being an aldehyde function or                     a hydroxymethyl function, or                 -   a compound A12 comprising at least one aldehyde                     function, or                 -   a mixture of a compound A11 and of a compound A12,                     and             -   at least one phenol A21,     -   means for creating a potential difference between the adhesive         composition and the conductive element.

The invention also relates to a coated conductive element which may be obtained via the process as defined previously.

The invention also relates to an elastomeric composite reinforced with at least one coated conductive element as defined previously, comprising an elastomeric matrix in which the coated conductive element is embedded.

The invention also relates to a tyre comprising at least one coated conductive element as defined previously or an elastomeric composite as defined previously.

The invention also relates to a belt comprising at least one coated conductive element as defined previously or an elastomeric composite as defined previously.

Finally, the invention relates to the use of an adhesive composition comprising:

-   -   at least one phosphate salt and     -   at least one resin based on:         -   at least one compound A1, compound A1 being chosen from:             -   a compound A11 comprising at least two functions, one of                 these functions being a hydroxymethyl function and the                 other being an aldehyde function or a hydroxymethyl                 function, or             -   a compound A12 comprising at least one aldehyde                 function, or             -   a mixture of a compound A11 and of a compound A12, and         -   at least one phenol A21,             for coating, by electroplating, an adhesive layer based on             the adhesive composition onto a conductive element.

The process according to the invention allows an appreciable increase in the service life of the composites according to the invention, and thus of the tyres or belts including them, notably under wet conditions demonstrating the corrosion resistance of the adhesive interface created.

The term “conductive element” means that the object is electrically conductive. In a preferential embodiment, the conductive element may thus be metallic.

The term “layer directly coating an object” means that the layer is in contact with the object without any other object, notably another layer, being interposed between the two.

The term “phr” means parts by weight per hundred parts of elastomer.

Furthermore, any range of values denoted by the expression “between a and b” represents the range of values extending from more than “a” to less than “b” (i.e. limits a and b excluded), while any range of values denoted by the expression “from a to b” means the range of values extending from “a” up to “b” (i.e. including the strict limits a and b).

Within the context of the invention, the carbon-based products mentioned in the description may be of fossil or biosourced origin. In the latter case, they may partially or completely result from biomass or be obtained from renewable starting materials derived from biomass.

In the present description, unless expressly indicated otherwise, all the percentages (%) shown are mass percentages.

The term “elastomeric composition” means a composition comprising at least one elastomer (or, equally, rubber) and at least one other constituent.

The term “diene” elastomer (or, equally, rubber) means an elastomer resulting at least partly (i.e. a homopolymer or a copolymer) from diene monomer(s) (i.e., monomers bearing two conjugated or non-conjugated carbon-carbon double bonds). The term “isoprene elastomer” means an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IRs), various isoprene copolymers and mixtures of these elastomers.

The term “elastomeric matrix” means a matrix having elastomeric behaviour.

The term “meta position relative to each other” means that the hydroxyl functions are borne by carbons of the aromatic nucleus which are separated from each other by a single other carbon of the aromatic nucleus.

The term “in the position ortho to a function” means the position occupied by the carbon of the aromatic nucleus which is immediately adjacent to the carbon of the aromatic nucleus bearing the function.

The term “member” of a nucleus means a constituent atom of the backbone of the nucleus. Thus, for example, a benzene nucleus comprises six members, each member consisting of a carbon atom. In another example, a furan nucleus comprises five members, four members each consisting of a carbon atom and the remaining member consisting of an oxygen atom.

“CHO” represents the aldehyde function.

“CH2OH” represents the hydroxymethyl function.

The term “aromatic polyphenol” means an aromatic compound comprising at least one benzene nucleus bearing more than one hydroxyl function.

The term “resin based on” should be understood as meaning that the resin includes the mixture and/or product of reaction of the various base constituents used for this resin as is defined above and that this resin is solely based on the constituents based on the resin. Thus, the base constituents are the reagents intended to react together during the final condensation of the resin and are not reagents intended to react together to form these base constituents.

In accordance with the invention, the base constituents thus comprise at least one compound A1 and at least one phenol A21. In one embodiment, the base constituents can comprise other additional constituents different from compound A1 and from the phenol A21. In another embodiment, the base constituents are constituted of at least one compound A1 and of at least one phenol A21.

Preferably, in the embodiment in which the base constituents comprise other additional constituents, these other additional constituents are free of formaldehyde and/or free of methylene donor chosen from the group consisting of hexamethylenetetramine (HMT), hexamethoxymethylmelamine (H3M), hexaethoxymethylmelamine, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, polymers of hexamethoxymethylmelamine of trioxane of formaldehyde, hexakis(methoxymethyl)melamine, N,N′,N″-trimethyl-N,N′,N″-trimethylolmelamine, hexamethylolmelamine, N-methylolmelamine, N,N′-dimethylolmelamine, N,N′,N″-tris(methoxymethyl)melamine, N,N′,N″-tributyl-N,N′,N″-trimethylolmelamine. More advantageously, these other additional constituents are free of formaldehyde and free of the methylene donors described in this paragraph.

More preferably, in the embodiment in which the base constituents comprise other additional constituents, these other additional constituents are free of formaldehyde and/or free of methylene donor chosen from the group consisting of hexamethylenetetramine, hexaethoxymethylmelamine, hexamethoxymethylmelamine, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, hexamethoxymethylmelamine of trioxane and the N-substituted oxymethylmelamines corresponding to the general formula:

in which Q represents an alkyl group containing from 1 to 8 carbon atoms; F₁, F₂, F₃, F₄ and F₅ are chosen, independently of each other, from the group consisting of a hydrogen atom, of an alkyl group containing from 1 to 8 carbon atoms, of the group —CH2OQ and the condensation products thereof. More advantageously, these other additional constituents are free of formaldehyde and free of the methylene donors described in this paragraph.

Even more preferably, in the embodiment in which the base constituents comprise other additional constituents, these other additional constituents are free of formaldehyde and/or free of methylene donor. More advantageously, these other additional constituents are free of formaldehyde and free of methylene donors.

The term “free of formaldehyde or free of methylene donor” means that the total mass content of formaldehyde or of methylene donor(s) belonging to the groups described above, relative to the total weight of the compound(s) A1 in the base constituents is less than or equal to 10%, preferably less than or equal to 5%, more preferentially less than or equal to 2% and even more preferentially less than or equal to 1%.

The term “free of formaldehyde or free of methylene donor” means that the total mass content of formaldehyde and of methylene donor(s) belonging to the groups described above, relative to the total weight of the compound(s) A1 in the base constituents, is less than or equal to 10%, preferably less than or equal to 5%, more preferentially less than or equal to 2% and even more preferentially less than or equal to 1%.

The term “adhesive layer based on” should, of course, be understood as meaning an adhesive layer including the mixture and/or the product of reaction of the various base constituents used to form the adhesive layer, in this instance the base constituents of the adhesive composition, it being possible for some of them to be intended to react or being capable of reacting with each other or with their immediate chemical surroundings, at least partly, during the various phases of manufacture of the adhesive layer, of the conductive reinforcement element or of the finished articles or composites, in particular during a curing step.

The term “solids content of the adhesive composition or an adhesive compound” means the mass of the adhesive composition or compound in g obtained after drying to the mass in g of the adhesive composition before drying. The solids content is measured in accordance with the standard NF EN 827 (March 2006).

Process According to the Invention

Preferably, the conductive element is immersed in the adhesive composition.

Advantageously, the conductive element is passed through the adhesive composition.

Advantageously, the conductive element is continuously unwound from a storage reel and the conductive element is passed continuously through the adhesive composition.

In one embodiment, the conductive element is connected to a potential that is higher than the potential to which the adhesive composition is connected.

Advantageously, the pH of the adhesive composition is basic, i.e. strictly greater than 7, so as firstly to obtain phenoxides in aqueous solution and secondly to facilitate the stabilization of the latices.

Preferably, the pH ranges from 8 to 14 and more preferentially from 9 to 12. This pH is measured under standard conditions, namely 23° C.±2° C. at atmospheric pressure according to the AFNOR standard NF T 90-008: Water quality—determination of the pH. A Mettler-Toledo Inlab 413 electrode is immersed into the solution and the value displayed after 2 minutes is then recorded.

Preferably, the adhesive composition comprises anionic surfactants for stabilizing the adhesive composition.

The conductive element may have any size and/or any geometrical shape. It may notably be filiform or in the form of a beam, a plate, a grate or a metal fabric.

In a preferred embodiment intended to be used in the tyre field, the conductive element is a conductive wire element.

Preferably, the conductive wire element comprises at least one elementary conductive monofilament. The or each elementary conductive monofilament is advantageously metallic. More preferentially, the or each elementary conductive monofilament comprises a steel core.

Advantageously, the water content of the adhesive composition is between 70% and 95% by weight and preferably between 75% and 90% by weight.

The solids content of the adhesive composition is between 5% and 30% by weight and preferably between 10% and 25% by weight.

The adhesive composition advantageously has a solids content of thermosetting resin and of latex between 5% and 60%, more preferentially between 10% and 30% by weight.

The term “solids content of the thermosetting resin and of latex” means the ratio between the mass of the thermosetting resin and of latex obtained after drying the aqueous adhesive composition to the mass of the aqueous adhesive composition before drying.

The solids content of the elastomeric latex (latices) in the aqueous adhesive composition ranges from 3.0% to 29.0%, preferably from 11.0% to 24.0% and more preferentially from 13.0% to 21.0%.

The weight ratio of the resin solids to latex solids is preferably between 0.1 and 2.0.

The adhesive composition of the electroplating process thus comprises at least one (i.e. one or more) phosphate salt and at least one (i.e. one or more) resin, this resin being based:

-   -   on at least one (i.e. one or more) compound A1, the compound A1         being chosen from:         -   a compound A11 comprising at least two functions, one of             these functions being a hydroxymethyl function and the other             being an aldehyde function or a hydroxymethyl function, or         -   a compound A12 comprising at least one aldehyde function, or         -   a mixture of a compound A11 and of a compound A12; and     -   on at least one (i.e. one or more) phenol A21.

In one preferential embodiment, the adhesive composition of the electroplating process thus comprises at least one (i.e. one or more) phosphate salt and at least one (i.e. one or more) resin; this resin being based on at least one (i.e. one or more) compound A11 and at least one (i.e. one or more) phenol A21.

In another preferential embodiment, the adhesive composition of the electroplating process thus comprises at least one (i.e. one or more) phosphate salt and at least one (i.e. one or more) resin; this resin being based on at least one (i.e. one or more) compound A12 and at least one (i.e. one or more) phenol A21.

In yet another embodiment, the adhesive composition of the electroplating process thus comprises at least one (i.e. one or more) phosphate salt and at least one (i.e. one or more) resin; this resin being based on at least one (i.e. one or more) compound A11 and at least one (i.e. one or more) compound A12 and at least one (i.e. one or more) phenol A21.

Phosphate Salt

An essential constituent of the adhesive composition is a phosphate salt.

Advantageously, the phosphate salt is chosen from sodium phosphate, potassium phosphate and mixtures of these phosphates and is preferably sodium phosphate.

Sodium phosphate is the compound which, in solid form, has the formula Na₃PO₄ and potassium phosphate is the compound which, in solid form, has the formula K₃PO₄.

The sodium and potassium phosphate salts have the advantage of being water-soluble under standard temperature and pressure conditions. Thus, these phosphate salts are soluble in the aqueous adhesive composition in a mass content of greater than or equal to 1 g/L in the aqueous adhesive composition, preferably 10 g/L. This solubility is measured under standard conditions, namely 23° C. at atmospheric pressure, by means of the following protocol. The aqueous adhesive composition comprising all of its constituents except for the phosphate salt(s) whose solubility it is desired to measure is prepared. Exactly approximately X g of solid to be measured are weighed out on a precision balance (0.0001 g). The solid is then placed in a conical flask and the aqueous adhesive composition prepared is gradually added to the conical flask with stirring. Once the solid is visibly dissolved, the final volume V of the aqueous adhesive composition prepared is measured. The ratio of the mass X to the volume V indicates the solubility.

Preferably, the composition is free of zinc phosphate dispersant and free of zinc phosphate.

More preferentially, the adhesive composition is free of agent for dispersing a water-insoluble phosphate salt and free of water-insoluble phosphate salts. In this more preferential embodiment, all the phosphate salts of the adhesive composition are water-soluble.

The term “agent for dispersing a salt in water” means a compound which has the property of keeping particles of this salt suspended in water and of ensuring the stability of the composition.

In a preferred embodiment, the adhesive composition does not comprise any phosphate salts other than the salts chosen from sodium phosphate, potassium phosphate and mixtures of these phosphates.

In a first embodiment in which the phosphate salt is sodium phosphate, the sodium phosphate is mixed so that the sodium phosphate solids content in the aqueous adhesive composition is less than or equal to 2.50%, preferably less than or equal to 2.00%, more preferentially less than or equal to 1.50% and even more preferentially less than or equal to 1.00%.

In this same first embodiment in which the phosphate salt is sodium phosphate, the sodium phosphate is mixed so that the sodium phosphate solids content in the aqueous adhesive composition is greater than or equal to 0.40%, preferably greater than or equal to 0.60%.

Very advantageously, the tribasic phosphate Na₃PO₄ has a buffer effect and makes it possible to maintain a pH ranging from 9 to 11.5. The tribasic phosphate Na₃PO₄ thus provides the adhesive composition with pH stability.

In a second embodiment in which the phosphate salt is potassium phosphate, the potassium phosphate is mixed so that the potassium phosphate solids content in the aqueous adhesive composition is less than or equal to 3.00%, preferably less than or equal to 2.50%, more preferentially less than or equal to 2.00% and even more preferentially less than or equal to 1.50%.

In this same second embodiment in which the phosphate salt is potassium phosphate, the potassium phosphate is mixed so that the potassium phosphate solids content in the aqueous adhesive composition is greater than or equal to 0.50%, preferably greater than or equal to 0.80%.

In a third embodiment in which the phosphate salt is a mixture of sodium phosphate and potassium phosphate, the sodium phosphate and potassium phosphate are mixed so that the potassium phosphate solids content in the aqueous adhesive composition is less than or equal to 3.00%, preferably less than or equal to 2.50%, very preferentially less than or equal to 2.00%, more preferentially less than or equal to 1.50% and even more preferentially less than or equal to 1.00%.

In this same third embodiment in which the phosphate salt is a mixture of sodium phosphate and potassium phosphate, the sodium phosphate and potassium phosphate are mixed so that the potassium phosphate solids content in the aqueous adhesive composition is greater than or equal to 0.40%, preferably greater than or equal to 0.50%, very preferentially greater than or equal to 0.60% and more preferentially greater than or equal to 0.80%.

Compound A1

Another essential constituent of the adhesive composition is a compound A1, compound A1 being chosen from:

-   -   a compound A11 comprising at least two functions, one of these         functions being a hydroxymethyl function and the other being an         aldehyde function or a hydroxymethyl function, or     -   a compound A12 comprising at least one aldehyde function, or     -   a mixture of a compound A11 and of a compound A12.

In accordance with the invention, the resin is based on at least one (i.e. one or more) compound A1.

In a first embodiment, compound A12 comprises at least one aromatic nucleus bearing at least one aldehyde function.

More preferentially, compound A12 bears at least two aldehyde functions.

Even more preferentially, the aromatic nucleus of compound A12 bears two aldehyde functions.

In one embodiment, the aromatic nucleus of compound A12 is chosen from the group consisting of a benzene nucleus and a furan nucleus; preferably, the aromatic nucleus of the aromatic aldehyde is a benzene nucleus.

Preferably, compound A12 is chosen from the group consisting of 1,2-benzenedicarboxaldehyde, 1,3-benzenedicarboxaldehyde, 1,4-benzenedicarboxaldehyde, 2-hydroxybenzene-1,3,5-tricarbaldehyde and mixtures of these compounds.

In one variant of the first embodiment, compound A12 has the general formula (A):

-   -   in which:     -   X comprises N, S or O,     -   R represents —H or —CHO.

Preferentially, compound A12 has the general formula (A′):

Even more preferentially, R represents —CHO.

According to a preferred embodiment, X represents O.

In one variant of compound A12 of general formula (A), X represents O and R represents —H. The compound A12 used is then of formula (Ba):

In a variant of the aldehyde of general formula (A′), X represents O and R represents —H. The compound A12 used is then furfuraldehyde and has the formula (B′a):

In another variant of compound A12 of general formula (A′), X represents O and R represents —CHO. The compound A12 used then has the formula (Bb):

In another variant of compound A12 of general formula (A′), X represents O and R represents —CHO. The compound A12 used is then 2,5-furandicarboxaldehyde and has the formula (B′b):

In another embodiment, X comprises N.

Preferably, compound A12 is chosen from the group consisting of furfuraldehyde, 2,5-furandicarboxaldehyde the mixtures of these compounds.

In one variant of compound A12 of general formula (A), X represents NH. The compound A12 used has the formula (Ca):

In one variant of compound A12 of general formula (A′), X represents NH. The compound A12 used has the formula (C′a):

Preferably, R represents —CHO in the variant of compound A12 of formula (C′a) and the compound A12 obtained is then 1H-pyrrole-2,5-dicarboxaldehyde.

In another variant of compound A12 of general formula (A), X represents NT₁ with T₁ representing an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group. The compound A12 used has the formula (Cb):

In another embodiment, X comprises S.

In one variant of compound A12 of general formula (A), X represents S. The compound A12 used has the formula (Da):

In one variant of compound A12 of general formula (A′), X represents S. The compound A12 used has the formula (D′a):

Preferably, R represents —CHO in the variant of compound A12 of formula (IV′a) and is then 2,5-thiophenedicarboxaldehyde.

In another variant of compound A12 of general formula (A), X represents ST₂ with T₂ representing an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group. The compound A12 used has the formula (Db):

In yet another variant of compound A12 of general formula (A), X represents T₃-S-T₂ with T₂ and T₃ each representing, independently of each other, an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group. The compound A12 used has the formula (Dc):

In yet another variant of compound A12 of general formula (A), X represents S═O. The compound A12 used has the formula (Dd):

In yet another variant of compound A12 of general formula (A), X represents O═S═O. The compound A12 used has the formula (De):

Among the various embodiments described above, preference will be given to the embodiments and variants in which X represents NH, S or O. In these embodiments and variants, it will be possible to have R representing —H or —CHO and preferably R representing —CHO. In these embodiments and variants, R will preferentially be in the 5 position and the —CHO group will preferentially be in the 2 position on the aromatic nucleus (general formula (A′)).

In a second embodiment, compound A11 is an aromatic compound comprising at least one aromatic nucleus bearing at least two functions, one of these functions being a hydroxymethyl function and the other being an aldehyde function or a hydroxymethyl function.

Thus, in this second embodiment, it is said aromatic nucleus which bears hydroxymethyl and aldehyde functions. Compound A11 thus corresponds, in this second embodiment, to the general formula (I):

HO—CH₂—Ar—B   (I)

in which Ar represents an aromatic nucleus and B represents CHO or CH₂OH.

The aromatic nucleus is advantageously a 5- or 6-membered nucleus comprising, as members, carbon atoms and optionally one or more heteroatoms, in particular nitrogen, oxygen or sulfur atoms, optionally oxidized in the N-oxide or S-oxide form. In one variant, the aromatic nucleus comprises 0, 1 or 2 heteroatom(s). The remainder of the aromatic nucleus may be substituted or unsubstituted.

The aromatic nucleus may bear 0, 1 or 2 aldehyde functions, advantageously 0 or 1 aldehyde function.

The aromatic nucleus may bear 1, 2 or 3 hydroxymethyl functions, advantageously 1 or 2 hydroxymethyl functions.

In addition, the aromatic nucleus may also bear 0, 1 or 2 other function(s), in particular hydroxyl function(s).

In the embodiment in which the aromatic nucleus is a 6-membered nucleus, the B and hydroxymethyl functions are advantageously in the meta or para position relative to each other.

In the embodiment in which the aromatic nucleus is a 5-membered nucleus, the nucleus may comprise one or more heteroatoms, in particular nitrogen, oxygen or sulfur atoms, optionally oxidized in the N-oxide or S-oxide form. Advantageously, the aromatic nucleus comprises 1 or 2 heteroatom(s), preferably 1 heteroatom.

In this embodiment, in which the aromatic nucleus is a 5-membered nucleus, at least one of the following three conditions is met:

-   -   the aromatic nucleus comprises 0 or a single aldehyde function;     -   the aromatic nucleus comprises one or two hydroxymethyl         functions;     -   apart from the aldehyde and hydroxymethyl functions, the         remainder of the aromatic nucleus is unsubstituted.

Advantageously, these three conditions are met.

In a first case, the aromatic nucleus comprises:

-   -   a single aldehyde function;     -   a single hydroxymethyl function;     -   apart from the aldehyde and hydroxymethyl functions, the         remainder of the aromatic nucleus is unsubstituted.

In a second case, the aromatic nucleus comprises:

-   -   0 aldehyde functions;     -   two hydroxymethyl functions;     -   apart from the hydroxymethyl functions, the remainder of the         aromatic nucleus is unsubstituted.

Advantageously, compound A11 corresponds to the general formula (II):

in which B represents CHO or CH₂OH, Y represents O, NR₁, NO, S, SO, SO₂ or SR₂R₃, R₁ represents a hydrogen or an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group and R₂ and R₃ each represent, independently of each other, a hydrogen or an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group.

Advantageously, compound A11 has the general formula (II′):

in which Y and B are as defined previously.

In a particularly advantageous embodiment, B represents CHO. In another embodiment, B represents CH₂OH.

According to a preferential embodiment, Y represents O.

In one variant, compound A11 has the formula (IIa):

B being as defined previously.

More particularly, compound A11 corresponds to the general formula (II′a1) or (II′a2):

5-(Hydroxymethyl)furfural (II′a1) is a particularly suitable compound, given that this organic compound can be readily derived from renewable resources. Specifically, it is derived notably from the dehydration of certain sugars, such as fructose, glucose, sucrose, cellulose and insulin.

In another embodiment, Y represents NR₁ or NO, advantageously NR₁. R₁ represents a hydrogen or an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group.

In one variant, the compound is of formula (IIb):

B being as defined previously,

-   and more particularly of formula (II′b1) or (II′b2):

in which R₁ is as defined previously. Advantageously, R₁ represents a hydrogen or a C₁-C₆ alkyl group.

In another embodiment, Y represents S, SO, SO₂ or SR₂R₃ with R₂ and R₃ as defined previously.

In one variant, the compound is of formula (IIc):

-   B being as defined previously,

with Y represents S, SR₂R₃, SO or SO₂ and R₂ and R₃ each represent, independently of each other, a hydrogen or an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group, B, R₂ and R₃ being as defined previously;

-   and more particularly of formula (II′c1) or (II′c2):

in which Y represents S, SR₂R₃, SO or SO₂ and R₂ and R₃ each represent, independently of each other, a hydrogen or an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group.

The compound may thus be:

Advantageously, R₂ and R₃ each represent, independently of each other, a C₁-C₆ alkyl radical.

The compound is advantageously of formula (II′c3) or (II′c4).

In another variant, the aromatic nucleus is a 6-membered nucleus, which may comprise 0, one or more heteroatoms, in particular nitrogen, optionally oxidized in N-oxide form. In one variant, the aromatic nucleus comprises 0, 1 or 2 heteroatom(s).

The B and hydroxymethyl functions are advantageously in the meta or para position relative to each other.

The aromatic nucleus may bear 0, 1 or 2 aldehyde functions, advantageously 0 or 1 aldehyde function.

The aromatic nucleus may bear 1, 2 or 3 hydroxymethyl functions, advantageously 1 or 2 hydroxymethyl functions.

In addition, the aromatic nucleus may also bear 0, 1 or 2 other function(s), in particular hydroxyl function(s).

Advantageously, compound A11 has the general formula (III):

in which Y represents C or NR₁, n has the value 0, 1 or 2, m has the value 0 or 1 and p has the value 1, 2 or 3. R₁ represents a hydrogen or an alkyl, aryl, arylalkyl, alkylaryl or cycloalkyl group. Thus, p+n>1 with p>0.

Advantageously, R₁ represents a hydrogen or a C₁-C₆ alkyl group.

In one variant, n has the value 1, m has the value 0 and p has the value 1.

In another variant, n has the value 1, m has the value 1 and p has the value 1.

In another variant, n has the value 2, m has the value 1 and p has the value 1.

In another variant, n has the value 1, m has the value 1 and p has the value 2.

In another variant, n has the value 0, m has the value 0 and p has the value 2.

In another variant, n has the value 0, m has the value 1 and p has the value 2.

In another variant, n has the value 1, m has the value 1 and p has the value 2.

In another variant, n has the value 0, m has the value 1 and p has the value 3.

Preferentially, the aromatic nucleus of compound A11 is a benzene nucleus. More preferentially, this aldehyde is chosen from the group consisting of 2-hydroxymethylbenzene-1-carboxaldehyde, 3-hydroxymethylbenzene-1-carboxaldehyde, 4-hydroxymethylbenzene-1-carboxaldehyde, 3-hydroxymethyl-6-hydroxybenzene-1-carboxaldehyde, 3-hydroxymethyl-4-hydroxybenzene-1-carboxaldehyde, 3-hydroxymethyl-2-hydroxybenzene-1-carboxaldehyde, 3-hydroxymethyl-2-hydroxybenzene-1,5-dicarboxaldehyde, 5-hydroxymethyl-2-hydroxybenzene-1,3-dicarboxaldehyde, 3,5-hydroxymethyl-4-hydroxybenzene-1-carboxaldehyde, 3,5-hydroxymethyl-2-hydroxybenzene-1-carboxaldehyde, 1,2-hydroxymethylbenzene, 1,3-hydroxymethylbenzene, 1,4-hydroxymethylbenzene, 1,3-hydroxymethyl-6-hydroxybenzene, 1,3-hydroxymethyl-4-hydroxybenzene, 1,3-hydroxymethyl-2-hydroxybenzene, 1,3,5-hydroxymethyl-2-hydroxybenzene, 1,3-hydroxymethyl-6-hydroxybenzene, 1,3,5-hydroxymethyl-4-hydroxybenzene, 1,3,2-hydroxymethyl-2-hydroxybenzene and mixtures of these compounds.

Even more preferentially, compound A11 used is 1-hydroxymethylbenzene-4-carboxaldehyde of formula (IIIa) or 1,4-hydroxymethylbenzene of formula (IIIb):

Among the other advantages associated with the use of the compounds A11 and/or A12, it will be noted that the adhesive composition may be free of formaldehyde, the use of which it is desirable to reduce, indeed even to eliminate in the long run, in adhesive compositions, due to the recent change in European regulations regarding this type of compound. In addition, formaldehyde is a compound derived from oil, the use of which it is desired to avoid as much as possible for reasons of increased scarcity.

Phenol A21

In accordance with the invention, the resin is based on at least one (i.e. one or more) phenol A21.

Advantageously, the phenol A21 is chosen from:

-   -   an aromatic polyphenol A2 comprising at least one aromatic         nucleus bearing at least two hydroxyl functions in the meta         position relative to each other, the two positions ortho to at         least one of the hydroxyl functions being unsubstituted,     -   an aromatic monophenol A2′ comprising at least one six-membered         aromatic nucleus bearing a single hydroxyl function,         -   the two positions ortho to the hydroxyl function being             unsubstituted, or         -   at least one position ortho to and the position para to the             hydroxyl function being unsubstituted,     -   a mixture of A2 and A2′.

In one embodiment, the phenol is an aromatic polyphenol A2 including one or more aromatic nuclei. The aromatic polyphenol comprises at least one aromatic nucleus bearing at least two hydroxyl functions in the meta position relative to each other, the two positions ortho to at least one of the hydroxyl functions being unsubstituted.

In another embodiment, the phenol is an aromatic monophenol A2′ comprising at least one six-membered aromatic nucleus bearing a single hydroxyl function. On this aromatic monophenol, the two positions ortho to the hydroxyl function are unsubstituted, or else at least one position ortho to and the position para to the hydroxyl function are unsubstituted.

In yet another embodiment, the phenol is a mixture of the aromatic polyphenol A2 and of the aromatic monophenol A2′ as described above.

In accordance with the invention, the aromatic polyphenol A2 may be, in one embodiment, a simple aromatic polyphenol molecule comprising one or more aromatic nuclei, at least one of these aromatic nuclei, or even each aromatic nucleus, bearing at least two hydroxyl functions in the meta position relative to each other, the two positions ortho to at least one of the hydroxyl functions being unsubstituted.

Similarly, the aromatic monophenol A2′ may be, in one embodiment, a simple aromatic monophenol molecule comprising one or more six-membered aromatic nuclei, at least one of these six-membered aromatic nuclei, or even each six-membered aromatic nucleus, bearing a single hydroxyl function, the two positions ortho to the hydroxyl function are unsubstituted, or else at least one position ortho to and the position para to the hydroxyl function are unsubstituted.

Such simple molecules do not comprise any repeating units.

In accordance with the invention, the aromatic polyphenol A2 may be, in another embodiment, a precondensed resin based on:

-   -   at least one aromatic polyphenol comprising at least one         aromatic nucleus bearing at least two hydroxyl functions in the         meta position relative to each other, the two positions ortho to         at least one of the hydroxyl functions being unsubstituted; and     -   at least one compound comprising at least one aldehyde function         and/or at least one compound comprising at least two         hydroxymethyl functions borne by an aromatic nucleus.

Such a precondensed resin based on aromatic polyphenol is in accordance with the invention and comprises, unlike the simple molecule described above, a repeating unit. In the case in point, the repeating unit comprises at least one aromatic nucleus bearing at least two hydroxyl functions in the meta position relative to each other.

Similarly and in accordance with the invention, the aromatic monophenol A2′ may be, in another embodiment, a precondensed resin based on:

-   -   at least one aromatic monophenol comprising at least one         six-membered aromatic nucleus bearing a single hydroxyl         function:         -   the two positions ortho to the hydroxyl function are             unsubstituted, or         -   at least one position ortho to and the position para to the             hydroxyl function are unsubstituted;     -   at least one compound comprising at least one aldehyde function         and/or at least one compound comprising at least two         hydroxymethyl functions borne by an aromatic nucleus.

Such a precondensed resin based on aromatic monophenol is in accordance with the invention and comprises, unlike the simple molecule described above, a repeating unit. In the case in point, the repeating unit comprises at least one six-membered aromatic nucleus bearing a single hydroxyl function.

In another embodiment, the phenol A21 is a mixture of an aromatic polyphenol which forms a simple molecule and of a precondensed resin based on aromatic polyphenol.

In yet another embodiment, the phenol A21 is a mixture of an aromatic monophenol which forms a simple molecule and of a precondensed resin based on aromatic monophenol.

In the specific embodiments which follow, the aromatic nucleus or nuclei of the aromatic polyphenol and/or of the aromatic monophenol are described. For the sake of clarity, the “aromatic polyphenol” and/or the “aromatic monophenol” is described therein in its simple molecule form. This aromatic polyphenol and/or this aromatic monophenol will subsequently be able to be condensed and will in part define the repeating unit. The features of the precondensed resin are described in more detail hereinbelow.

Aromatic Polyphenol A2

In a preferred embodiment, the aromatic nucleus of the aromatic polyphenol bears three hydroxyl functions in the meta position relative to each other.

Preferably, the two positions ortho to each hydroxyl function are unsubstituted. This is understood to mean that the two carbon atoms located on either side of (in the position ortho to) the hydroxylated carbon atom (i.e. the carbon atom bearing the hydroxyl function) bear a simple hydrogen atom.

Even more preferably, the remainder of the aromatic nucleus of the aromatic polyphenol is unsubstituted. This is understood to mean that the other carbon atoms of the remainder of the aromatic nucleus (those other than the carbon atoms bearing the hydroxyl functions) bear a simple hydrogen atom.

In one embodiment, the aromatic polyphenol comprises several aromatic nuclei, at least two of them each bearing at least two hydroxyl functions in the meta position relative to each other, the two positions ortho to at least one of the hydroxyl functions of at least one aromatic nucleus being unsubstituted.

In a preferred embodiment, at least one of the aromatic nuclei of the aromatic polyphenol bears three hydroxyl functions in the meta position relative to each other.

Preferably, the two positions ortho to each hydroxyl function of at least one aromatic nucleus are unsubstituted.

Even more preferably, the two positions ortho to each hydroxyl function of each aromatic nucleus are unsubstituted.

Advantageously, the, or each, aromatic nucleus of the aromatic polyphenol is a benzene nucleus.

As examples of aromatic polyphenols including just one aromatic nucleus, mention may be made in particular of resorcinol and phloroglucinol, as a reminder of structural formulae (IV) and (V), respectively:

By way of example, in the case where the aromatic polyphenol includes several aromatic nuclei, at least two of these aromatic nuclei, which may be identical or different, are chosen from those of general formulae:

in which the symbols Z₁ and Z₂, which may be identical or different, if there are several of them on the same aromatic nucleus, represent an atom (for example, carbon, sulfur or oxygen) or a bonding group, by definition at least divalent, which connects at least these two aromatic nuclei to the remainder of the aromatic polyphenol.

Another example of an aromatic polyphenol is 2,2′,4,4′-tetrahydroxydiphenyl sulfide of structural formula (VII) below:

Another example of an aromatic polyphenol is 2,2′,4,4′-tetrahydroxydiphenyl benzophenone of structural formula (VIII) below:

It is noted that each compound VII and VIII is an aromatic polyphenol including two aromatic nuclei (of formulae VI-c), each of which bears at least two (in this instance two) hydroxyl functions in the meta position relative to each other.

It is noted, in the case of an aromatic polyphenol including at least one aromatic nucleus in accordance with formula VI-b, that the two positions ortho to each hydroxyl function of at least one aromatic nucleus are unsubstituted. In the case of an aromatic polyphenol including several aromatic nuclei in accordance with formula VI-b, the two positions ortho to each hydroxyl function of each aromatic nucleus are unsubstituted.

According to one embodiment of the invention, the aromatic polyphenol is chosen from the group consisting of resorcinol (IV), phloroglucinol (V), 2,2′,4,4′-tetrahydroxydiphenyl sulfide (VII), 2,2′,4,4′-tetrahydroxybenzophenone (VIII) and mixtures of these compounds. In a particularly advantageous embodiment, the aromatic polyphenol is phloroglucinol.

In one embodiment, the aromatic polyphenol A2 comprises a precondensed resin based on the aromatic polyphenol as described in any one of these embodiments.

This precondensed resin is advantageously based on:

-   -   at least one aromatic polyphenol as defined previously, and         preferably chosen from the group consisting of resorcinol,         phloroglucinol, 2,2′,4,4′-tetrahydroxydiphenyl sulfide,         2,2′,4,4′-tetrahydroxybenzophenone and mixtures thereof; and     -   at least one compound capable of reacting with the aromatic         polyphenol comprising at least one aldehyde function and/or at         least one compound capable of reacting with the aromatic         polyphenol comprising at least two hydroxymethyl functions, and         preferentially an aromatic aldehyde comprising at least one         aromatic nucleus bearing at least one aldehyde function.

The compound that is capable of reacting with the aromatic polyphenol with compound A1 may be an aromatic compound as defined previously or any other aldehyde. Advantageously, said compound is chosen from the group consisting of an aromatic compound comprising an aromatic nucleus bearing at least two functions, one of these functions being a hydroxymethyl function, the other being an aldehyde function or a hydroxymethyl function, formaldehyde, furfuraldehyde, 2,5-furandicarboxaldehyde, 1,4-benzenedicarboxaldehyde, 1,3-benzenedicarboxaldehyde, 1,2-benzenedicarboxaldehyde and mixtures of these compounds. Very advantageously, when the compound that is capable of reacting with the aromatic polyphenol is an aromatic compound comprising an aromatic nucleus bearing at least two functions, one of these functions being a hydroxymethyl function and the other being an aldehyde function or a hydroxymethyl function, this compound is chosen from the group consisting of 5-(hydroxymethyl)furfural, 2,5-di(hydroxymethyl)furan and mixtures of these compounds.

Thus, in the precondensed resin based on aromatic polyphenol, the repeating unit corresponds to the features of the aromatic polyphenol defined previously except that at least one of the carbon atoms of the aromatic nucleus, which was unsubstituted, is connected to another unit.

Irrespective of the compound other than the aromatic polyphenol which is the basis of the precondensed resin, this precondensed resin is devoid of free formaldehyde. This is because, even in the case where the precondensed resin is based on an aromatic polyphenol as described previously and on formaldehyde, since the formaldehyde has already reacted with the aromatic polyphenol, the precondensed resin is devoid of free formaldehyde liable to be able to react with a compound A1 in accordance with the invention in a subsequent step.

The aromatic polyphenol A2 may also comprise a mixture of a free aromatic polyphenol molecule and of a precondensed resin based on aromatic polyphenol, as described previously. In particular, the aromatic polyphenol A2 may also comprise a mixture of phloroglucinol and of a precondensed resin based on phloroglucinol.

Aromatic Monophenol A2′

The aromatic monophenol A2′ may be in accordance with two variants. In one variant, the two positions ortho to the hydroxyl function are unsubstituted. In another variant, at least one position ortho to and the position para to the hydroxyl function are unsubstituted.

Advantageously, in the variant in which at least one position ortho to and the position para to the hydroxyl function are unsubstituted, a single ortho position is unsubstituted and the position para to the hydroxyl function is unsubstituted.

Preferably, whatever the variant, the two positions ortho to the hydroxyl function are unsubstituted. This is understood to mean that the two carbon atoms located on either side of (in the position ortho to) the hydroxylated carbon atom (i.e. the carbon atom bearing the hydroxyl function) bear a simple hydrogen atom.

Even more preferentially, the remainder of the aromatic nucleus is unsubstituted. This is understood to mean that the other carbon atoms of the remainder of the aromatic nucleus (those other than the carbon atoms bearing the hydroxyl functions) bear a simple hydrogen atom.

In one embodiment, the aromatic monophenol comprises several six-membered aromatic nuclei, at least two of them each bearing a single hydroxyl function and, for at least one of the hydroxyl functions, the two positions ortho to the hydroxyl function are unsubstituted or at least one position ortho to and the position para to the hydroxyl function are unsubstituted.

Preferably, the two positions ortho to each hydroxyl function of at least one six-membered aromatic nucleus are unsubstituted.

Even more preferentially, the two positions ortho to each hydroxyl function of each six-membered aromatic nucleus are unsubstituted.

Even more preferentially, the remainder of each of the aromatic nuclei is unsubstituted. This is understood to mean that the other carbon atoms of the remainder of each aromatic nucleus (those other than the carbon atoms bearing the hydroxyl functions or bearing the group which connects the aromatic nuclei together) bear a simple hydrogen atom.

Advantageously, the or each aromatic nucleus of the aromatic monophenol is a benzene nucleus.

Preferably, the aromatic monophenol is chosen from the group consisting of phenol, ortho-cresol, meta-cresol, para-cresol, ortho-chlorophenol, meta-chlorophenol, para-chlorophenol, 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 4-vinylphenol, 4-ethylphenol, 4-isopropylphenol, 4-isobutylphenol, para-coumaric acid and mixtures of these compounds.

In one embodiment, the aromatic monophenol A2′ comprises a precondensed resin based on the aromatic monophenol as described in any one of these embodiments.

This precondensed resin is advantageously based on:

-   -   at least one aromatic monophenol as defined previously, and         preferentially chosen from the group consisting of phenol,         ortho-cresol, meta-cresol, para-cresol, ortho-chlorophenol,         meta-chlorophenol, para-chlorophenol, 2-hydroxybenzoic acid,         3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 4-vinylphenol,         4-ethylphenol, 4-isopropylphenol, 4-isobutylphenol,         para-coumaric acid, and mixtures of these compounds; and     -   at least one compound that is capable of reacting with the         aromatic monophenol comprising at least one aldehyde function         and/or at least one compound that is capable of reacting with         the aromatic monophenol comprising at least two hydroxymethyl         functions, and preferentially an aromatic aldehyde comprising at         least one aromatic nucleus bearing at least one aldehyde         function.

The compound that is capable of reacting with the aromatic monophenol may be a compound A1 as defined previously or any other aldehyde. Advantageously, said compound that is capable of reacting with the aromatic polyphenol is chosen from the group consisting of an aromatic compound comprising an aromatic nucleus bearing at least two functions, one of these functions being a hydroxymethyl function, the other being an aldehyde function or a hydroxymethyl function, formaldehyde, furfuraldehyde, 2,5-furandicarboxaldehyde, 1,4-benzenedicarboxaldehyde, 1,3-benzenedicarboxaldehyde, 1,2-benzenedicarboxaldehyde and mixtures of these compounds. Very advantageously, when the compound is an aromatic compound comprising an aromatic nucleus bearing at least two functions, one of these functions being a hydroxymethyl function and the other being an aldehyde function or a hydroxymethyl function, this compound is chosen from the group consisting of 5-(hydroxymethyl)furfural, 2,5-di(hydroxymethyl)furan and mixtures of these compounds.

Thus, in the precondensed resin based on aromatic monophenol, the repeating unit corresponds to the features of the aromatic monophenol defined above except that at least one of the carbon atoms of the six-membered aromatic nucleus, which was unsubstituted, is connected to another unit.

Whatever the compound other than the aromatic monophenol that is the basis of the precondensed resin, this precondensed resin is devoid of free formaldehyde. This is because, even in the case where the precondensed resin is based on an aromatic monophenol as described previously and on formaldehyde, since the formaldehyde has already reacted with the aromatic monophenol, the precondensed resin is devoid of free formaldehyde liable to be able to react with a compound A1 in accordance with the invention in a subsequent step.

The aromatic monophenol A2′ may also comprise a mixture of a free aromatic monophenol molecule and of a precondensed resin based on aromatic monophenol, as described previously. In particular, the aromatic monophenol A2′ may also comprise a mixture of phenol and of a precondensed resin based on phenol.

Mixture of Aromatic Polyphenol A2 and of Aromatic Monophenol A2′

The phenol A21 may also comprise a mixture of an aromatic polyphenol A2 and of an aromatic monophenol A2′, as described previously.

Preferably, the phenol A21 comprises a mixture of an aromatic polyphenol and of a precondensed resin based on aromatic polyphenol.

Elastomeric Latex

The adhesive composition may optionally comprise an elastomeric latex, which is preferably unsaturated. Such an elastomeric latex makes it possible to provide an elastomeric physical interface when the adhesive composition is used for coating elements intended to be embedded in an elastomeric matrix. When the elastomeric latex is unsaturated, it also provides a chemical interface by means of the unsaturations capable of forming bridges with the crosslinking system of the elastomeric matrix.

It is recalled that a latex is a stable dispersion of microparticles of elastomer(s) in suspension in a generally aqueous solution. An elastomeric latex is thus a composition in a liquid state comprising a liquid solvent, generally water, and at least one elastomer or a rubber dispersed in the liquid solvent so as to form a suspension. Thus, the latex is not a rubber composition which comprises a matrix of elastomer or of rubber in which at least one other component is dispersed. A rubber composition is in a plastic state in the uncured (non-crosslinked) state and in an elastic state in the cured (crosslinked) state, but never in a liquid state, unlike a latex.

Unsaturated (that is to say, bearing carbon-carbon double bonds) elastomer latices, notably diene elastomer latices, are well known to those skilled in the art. They notably form the elastomeric base of the RFL adhesives described in the introduction to the present specification.

The unsaturated elastomer of the latex is preferentially a diene elastomer, more preferentially a diene elastomer chosen from the group consisting of polybutadienes, butadiene copolymers, polyisoprenes, isoprene copolymers and mixtures of these elastomers. It is even more preferentially chosen from the group consisting of butadiene copolymers, vinylpyridine/styrene/butadiene terpolymers, natural rubber, and mixtures of these elastomers.

Process for Manufacturing a Precondensed Resin

N1 is defined as the number of reactive sites on the aromatic compound, as follows: an aldehyde function represents two reactive sites and a hydroxymethyl function represents one reactive site. Thus, for example, 5-(hydroxymethyl)furfural has N1=3 reactive sites and 2,5-di(hydroxymethyl)furan has N1=2 reactive sites.

In the case of an aromatic polyphenol, N2 is defined as the number of reactive sites of the aromatic polyphenol, as follows: each free carbon on the aromatic nucleus adjacent to a hydroxyl function borne by the aromatic nucleus represents a reactive site, each free carbon only being able to be counted as a reactive site for a single adjacent hydroxyl function. Thus, for example, resorcinol and phloroglucinol each have N2=3 reactive sites and 2,2′,4,4′-tetrahydroxydiphenyl sulfide has N2=4 reactive sites.

In the case of an aromatic monophenol, N′2 is defined as the number of reactive sites of the aromatic monophenol, as follows: each free carbon on the six-membered aromatic nucleus adjacent to the hydroxyl function borne by the aromatic nucleus represents a reactive site, and the free carbon of the six-membered aromatic nucleus positioned para to the hydroxyl function represents a reactive site. Thus, for example, phenol has N′2=3 reactive sites.

The precondensed resin is obtained by mixing:

-   -   compound A1 and     -   the aromatic polyphenol A2 and optionally     -   the aromatic monophenol A2′,         in a basic solvent preferably having a pH of between 8 and 13,         more preferentially between 9 and 12, or in an acidic or neutral         solvent preferably having a pH of between 4 and 7 and more         preferentially between 5 and 7.

The precondensed resin is advantageously prepared by gradually mixing the aromatic polyphenol and optionally the aromatic monophenol and compound A1 in an aqueous solution.

In a first variant, the components on which the precondensed resin is based are mixed in a basic solvent, such as an aqueous sodium hydroxide solution, preferably having a pH of between 8 and 13, more preferentially between 9 and 12.

In a second variant, the components on which the precondensed resin is based are mixed in an acidic or neutral solvent such as an aqueous solution having a pH of between 4 and 7, preferably between 5 and 7.

In some cases, for example at relatively high concentrations or in the case of an acidic solvent, a person skilled in the art may find cause to add a thickener, for example carboxymethylcellulose, or a gelling agent, for example a gelatin, in order to limit the sedimentation of the precondensed resin.

Regardless of the variant, the combined constituents are mixed with stirring for a time which may vary depending on the temperature used and the specific composition targeted, for example for a period of time which may vary between 1 min and 6 h, at a temperature of between 20° C. and 90° C., preferentially between 20° C. and 60° C.

In the first variant, an acid is advantageously subsequently added so as to neutralize the base and to obtain a precondensed resin that can be stored and used subsequently.

In the second variant, a base is advantageously subsequently added so as to neutralize the acid and to obtain a precondensed resin that can be stored and used subsequently.

In order to prepare the precondensed resin, the molar amount n2 of aromatic polyphenol A2, the molar amount n′2 of aromatic monophenol A2′ and the molar amount n1 of compound A1 are such that [(n2*N2)+(n′2N′2)]/(n1*N1)>1, preferably 1<[(n2*N2)+(n′2N′2))+(n′2N′2)]/(n1*N1)<5.

The precondensed resin is subsequently generally diluted in water.

In the final aqueous adhesive solution thus prepared, the solids content of precondensed resin according to the invention preferably represents between 2% and 30% by weight, more preferentially between 5% and 15% by weight.

The water content of the final aqueous adhesive solution thus prepared is preferably between 70% and 98% by weight, more preferentially between 85% and 95% by weight.

The term “water content of the aqueous adhesive solution” means the weight of water relative to the total weight of the adhesive solution.

Composition Manufacturing Process

The aqueous adhesive composition in accordance with the invention may of course comprise all or some of the additives customary for aqueous adhesive compositions, such as those used in conventional RFL adhesives; mention will be made, for example, of bases such as aqueous ammonia, sodium, potassium or ammonium hydroxide, dyes, fillers such as carbon black or silica, antioxidants or other stabilizers, and thickeners, for example carboxymethylcellulose, or gelling agents, for example a gelatin, making it possible to increase the viscosity of the composition. Mention will also be made of additives that make it possible to modify the setting or gelling time and the open time of the resin. As is known to those skilled in the art, the setting or gelling time is the length of time for which it is possible to apply the resin to its substrate and the open time is the length of time for which, after application of the resin to its substrate, it is possible to leave the resin in the open air without adversely affecting the quality of the subsequent adhesive bond with the complementary substrate. The setting time or gelling time and the open time are notably dependent on the temperature, pressure or else the resin concentration.

Typically, during a first resinification step, the constituents of the thermosetting resin itself are mixed, advantageously in water.

This first resinification step may be performed according to several embodiments.

Before describing in detail the various embodiments, it will first be specified that the thermosetting resin of the aqueous adhesive composition may be obtained by mixing the constituents of the resin, i.e. said compound A1 as defined previously, said aromatic compound A2 as defined previously and/or said aromatic compound A2′ as defined previously, in a basic solvent, preferably having a pH of between 8 and 13, more preferentially between 9 and 12.

In a first embodiment, use is made of a precondensed resin based on aromatic polyphenol A2 as defined previously, i.e. a resin based on:

-   -   at least one aromatic polyphenol comprising at least one         aromatic nucleus bearing at least two hydroxyl functions in the         meta position relative to each other, the two positions ortho to         at least one of the hydroxyl functions being unsubstituted; and     -   at least one compound that is capable of reacting with said         aromatic polyphenol comprising at least one aldehyde function         and/or at least one compound that is capable of reacting with         said aromatic polyphenol comprising at least two hydroxymethyl         functions borne by an aromatic nucleus.

The precondensed resin based on aromatic polyphenol A2 is advantageously prepared by gradually mixing the aromatic polyphenol and the compound comprising at least one aldehyde function and/or the compound comprising at least two hydroxymethyl functions borne by an aromatic nucleus, for example formaldehyde, in molar amounts as described previously.

In one variant, the components on which the precondensed resin is based are mixed in a basic solvent, such as an aqueous sodium hydroxide solution, preferably having a pH of between 8 and 13, more preferentially between 9 and 12.

Thus, the precondensed resin is obtained by mixing:

-   -   said aromatic polyphenol, and     -   said compound that is capable of reacting with said aromatic         polyphenol,         in a basic solvent preferably having a pH of between 8 and 13         and more preferentially between 9 and 12.

In some cases, for example at relatively high concentrations or in the case of an acidic solvent, a person skilled in the art may find cause to add a thickener, for example carboxymethylcellulose, or a gelling agent, for example a gelatin, in order to limit the sedimentation of the precondensed resin.

Regardless of the variant, the combined constituents are mixed with stirring for a time which may vary depending on the temperature used and the specific composition targeted, for example for a period of time which may vary between 1 min and 6 h, at a temperature of between 20° C. and 90° C., preferentially between 20° C. and 60° C.

As described previously, it is advantageously possible to neutralize the medium so as to obtain a precondensed resin that can be stored and used subsequently.

Then, in this first embodiment, the adhesive composition may be obtained by mixing:

-   -   this precondensed resin (compound A2), and         compound A1     -   in a basic solvent preferably having a pH of between 8 and 13         and more preferentially between 9 and 12.

In particular, this precondensed resin based on aromatic polyphenol (compound A2) and compound A1 are gradually mixed in a basic solvent, such as an aqueous sodium hydroxide solution, preferably having a pH of between 8 and 13, more preferentially between 9 and 12. All the constituents are mixed with stirring for a length of time which may vary depending on the temperature used and the specific composition targeted, for example for a time which may vary between 1 min and 6 h, at a temperature of between 20° C. and 90° C., preferentially between 20 and 60° C. A person skilled in the art will know how to adjust the molar amounts of the precondensed resin based on aromatic polyphenol A2 and on compound A1 in order to obtain crosslinking and a concentration suitable for the desired use, notably as a function of the nature of the precondensed resin based on aromatic polyphenol A2.

In a second embodiment, use is made of a precondensed resin as described previously, that is to say based on:

-   -   at least one compound A1, compound A1 being chosen from:         -   a compound A11 comprising at least two functions, one of             these functions being a hydroxymethyl function and the other             being an aldehyde function or a hydroxymethyl function, or         -   a compound A12 comprising at least one aldehyde function, or         -   a mixture of a compound A11 and of a compound A12; and     -   at least one aromatic polyphenol A2 comprising at least one         aromatic nucleus bearing at least two hydroxyl functions in the         meta position relative to each other, the two positions ortho to         at least one of the hydroxyl functions being unsubstituted, for         example phloroglucinol.

In this second embodiment, the precondensed resin based on aromatic polyphenol in accordance with the invention is prepared under conditions analogous to the precondensed resin based on aromatic polyphenol of the first embodiment. Then, this precondensed resin based on aromatic polyphenol according to the invention A2 is gradually mixed with compound Al under conditions analogous to those of the first embodiment. Here too, a person skilled in the art will know how to adjust the molar amounts of precondensed resin based on aromatic polyphenol A2 and on compound A1 in order to obtain crosslinking and a concentration suitable for the desired use, notably as a function of the nature of the precondensed resin based on aromatic polyphenol A2.

In a third embodiment, use is made of an aromatic polyphenol A2 according to the invention in the form of a single molecule, for example phloroglucinol.

In a first variant, the thermosetting resin is obtained by:

-   -   mixing the aromatic polyphenol A2 in the form of a single         molecule in a basic solvent preferably having a pH of between 8         and 13, more preferentially between 9 and 12,     -   then adding compound A1.

In particular, the aromatic polyphenol A2 is firstly mixed in a basic solvent, such as an aqueous sodium hydroxide solution, preferably having a pH of between 8 and 13, more preferentially between 9 and 12.

In some cases, for example at relatively high concentrations or in the case of an acidic solvent, a person skilled in the art may find cause to add a thickener, for example carboxymethylcellulose, or a gelling agent, for example a gelatin, in order to limit the sedimentation of the aromatic polyphenol A2.

Then, compound A1 is added. In particular, compound A1 is gradually added under conditions analogous to those of the first embodiment.

In a second variant, the thermosetting resin is obtained by:

-   -   mixing compound A1 in a basic solvent preferably having a pH of         between 8 and 13 and more preferentially between 9 and 12,     -   then adding the aromatic polyphenol A2 in the form of a single         molecule.

In particular, compound A1 is first mixed in an aqueous solution, preferably in a basic solvent, such as an aqueous sodium hydroxide solution, preferably having a pH of between 8 and 13, more preferentially between 9 and 12. Then, the aromatic polyphenol A2 is added and the components are mixed under conditions analogous to those of the first embodiment.

A molar amount n2 of aromatic polyphenol A2 and a molar amount n1 of compound A1 are mixed such that 0.3≤(n2*N2)/(n1*N1)≤3, and preferably 1<(n2*N2)/(n1*N1)≤2.

In each of the three preceding embodiments, the aromatic polyphenol could be entirely or partially replaced with an aromatic monophenol comprising at least one six-membered aromatic nucleus bearing a single hydroxyl function, the two positions ortho to the hydroxyl function being unsubstituted, or at least one position ortho to and the position para to the hydroxyl function being unsubstituted.

In this case, in the third embodiment described above, in which use is made of compounds in the form of single molecules, a molar amount n2 of aromatic polyphenol A2 and/or a molar amount n′2 of aromatic monophenol A2′ and a molar amount n1 of compound A1 would then be mixed such that 0.3≤[(n2*N2)+(n′2*N′2)]/(n1*N1)≤3, and preferably 1<[(n2*N2)+(n′2*N′2)]/(n1*N1)≤2.

In any one of these three embodiments, the partially crosslinked thermosetting resin is generally diluted in water before being added to the unsaturated elastomer latex or latices (if there are several), in order to form the aqueous adhesive composition of the invention, according to a general procedure which is well known to those skilled in the art in the field of RFL adhesives.

Preferably, during this step of forming the aqueous adhesive composition, it will be ensured that the aqueous adhesive composition has a pH of between 8 and 13, more preferentially between 9 and 12, so as to limit any potential precipitation of the, or of some, unsaturated elastomer latex (latices).

Thus, in the event that, during the resinification step preceding this step of forming the aqueous adhesive composition, use was made of an acidic or neutral solvent or a basic solvent which was neutralized, a base will be added that makes it possible to obtain a pH of between 8 and 13, more preferentially between 9 and 12, prior to the addition of the unsaturated elastomer latex (latices), so as to limit any potential precipitation of the, or of some, unsaturated elastomer latex (latices).

For example, the constituents of the adhesive composition are added in the following order: the water, possible water-soluble additives (for example aqueous ammonia), the latex or latices (in any order) and the partially crosslinked thermosetting resin (diluted).

The combination is mixed with stirring for 1 to 30 min, for example at 20° C.

During a final manufacturing step, referred to as maturation step, the aqueous adhesive composition is generally stored at room temperature (23° C.) for a maturation time which may typically range from 1 to several hours, indeed even several days, before it is finally used.

Electroplating Device According to the Invention

The invention also relates to an electroplating device as defined previously.

In one embodiment, the means for creating a potential difference comprise a current generator. In this embodiment, a current value is set so as to create the potential difference. As a variant, a voltage generator could be used so as to set the voltage value.

In a first variant, the positive terminal of the current generator is connected to the conductive element and the negative terminal of the current generator is connected to the adhesive composition.

In a second variant, the positive terminal of the current generator is connected to the adhesive composition and the negative terminal of the current generator is connected to the conductive element.

More preferentially, the means for creating a potential difference comprise at least one electrically conductive pulley, on contact with which the conductive element is capable of moving, the pulley being connected to the current generator so as to create a potential difference between the electrically conductive pulley and the adhesive composition.

Advantageously, the contact means comprise means for making the conductive element travel continuously through the adhesive composition.

Preferably, the continuous travel means comprise a tank containing the adhesive composition and means for unwinding and winding the conductive element, which are respectively placed upstream and downstream of the tank.

Conductive Element According to the Invention

The invention also relates to a coated conductive element as defined previously. Such a conductive element is coated by electroplating with an adhesive layer based on the adhesive composition.

The conductive element is an element of any size and/or any geometrical shape. It may notably be filiform or in the form of a beam, a plate, a grate or a metal fabric.

Preferably, the conductive element is a metal wire element.

Preferentially, the coated conductive wire element is obtained via the process according to the invention.

The conductive wire element may comprise, in one embodiment, a single elementary conductive monofilament. In another embodiment, the conductive wire element comprises several elementary conductive monofilaments assembled together, for example by braiding or twisting. Among the conductive wire elements comprising several elementary conductive monofilaments, examples that will be mentioned include layered cables and multistrand cables. Each elementary conductive monofilament is unitary, that is to say that the constituents of each elementary conductive monofilament are inseparable from each other.

Advantageously, the conductive wire element is a metal wire element. More preferentially, the or each elementary conductive monofilament is advantageously metallic. More preferentially, the or each elementary conductive monofilament comprises a steel core. The steel core is monolithic, that is to say that it is, for example, made as one piece or moulded.

The term “monofilament” means the longilinear elements of great length relative to their cross section, whatever their shape, for example circular, oblong, rectangular or square, or even flat, it being possible for this monofilament to be rectilinear or non-rectilinear, for example twisted or wavy. When it is of circular shape, the diameter of each monofilament is preferably less than 5 mm. Preferably, the or each monofilament has a circular cross section with a diameter of between 0.05 mm and 0.50 mm.

In one variant, the metal element is a strip, a band or a ribbon which has a great length relative to its thickness. The thickness of such metal elements is preferably less than 2 mm, more preferentially less than 1 mm. Even more preferentially, this thickness is between 0.1 and 0.8 mm, in particular in a range from 0.15 to 0.5 mm, even more particularly in a range from 0.2 to 0.5 mm, even more particularly in a range from 0.25 to 0.45 mm or in a range from 0.15 to 0.35 mm. The width of such metal elements is between 1 and 15 mm, more preferentially greater than 1 mm and less than or equal to 10 mm, even more preferentially in a range from 2.5 to 10 mm, even more preferentially from 2.5 to 5 mm.

In one embodiment, the adhesive layer directly coats the steel core of the or each elementary conductive monofilament. The adhesive layer coats at least a portion of the or each elementary conductive monofilament. Thus, the adhesive layer can partially or completely coat the or each elementary conductive monofilament. Thus, in the embodiment in which the conductive wire element comprises a single elementary conductive monofilament, the adhesive layer can coat some portions of this monofilament or else all of it. In the embodiment in which the conductive wire element comprises several elementary conductive monofilaments, the adhesive layer can coat several elementary conductive monofilaments without coating others, or else can coat solely certain portions of some or all of the elementary conductive monofilaments.

In another embodiment, the adhesive layer directly coats a layer of a conductive coating directly coating the steel core of the or each elementary conductive monofilament. The metal of the layer of the conductive coating is made from a metal other than steel.

In yet another embodiment, the adhesive layer directly coats a nonmetallic intermediate adhesive layer coating the steel core of the or each elementary conductive monofilament. In one variant of this embodiment, the nonmetallic intermediate adhesive layer directly coats the layer of the metallic coating directly coating the steel core of the or each conductive wire element. The nonmetallic intermediate layer, generally known as adhesion primer, makes it possible, in combination with the adhesive layer comprising the adhesive composition, to improve the adhesion of the conductive wire element to the elastomeric matrix.

In another embodiment, the adhesive layer directly coats a layer of a metallic coating directly coating the steel core of the or each elementary conductive monofilament with the adhesive layer. The metal of the layer of the metallic coating is made from a metal other than steel.

Preferably, the metal of the layer of the metallic coating directly coating at least a portion of the steel core of the or each elementary conductive monofilament is chosen from zinc, copper, tin and alloys of these metals. As examples of alloys of these metals, mention will be made of brass and bronze.

In yet another embodiment, the adhesive layer directly coats a nonmetallic intermediate adhesive layer coating the steel core of the or each elementary conductive monofilament. In one variant of this embodiment, the nonmetallic intermediate adhesive layer directly coats the layer of the metallic coating directly coating the steel core of the or each elementary conductive monofilament. The nonmetallic intermediate layer, generally known as adhesion primer, makes it possible, in combination with the adhesive layer comprising the adhesive composition, to improve the adhesion of the wire element to the elastomeric matrix. Such adhesion primers are those commonly used by a person skilled in the art for the presizing of certain textile fibres (in particular polyester, for example PET, aramid or aramid/nylon fibres). For example, use could be made of an epoxy-based primer, in particular a primer based on polyglycerol polyglycidyl ether. Use could also be made of a primer based on blocked isocyanate.

The steel may have a perlitic, ferritic, austenitic, bainitic or martensitic microstructure or a microstructure resulting from a mixture of these microstructures.

Preferably, the steel comprises a carbon content ranging from 0.2% to 1% by mass and more preferentially from 0.3% to 0.7% by mass.

In one embodiment, the steel used comprises less than 0.5%, preferably not more than 0.05%, limit included, and more preferentially not more than 0.02%, limit included, by mass of chromium.

In another embodiment using stainless steel, the steel comprises at least 0.5%, limit included, preferably at least 5%, limit included, and more preferentially at least 15%, limit included, by mass of chromium.

Composite According to the Invention

The invention also relates to an elastomeric composite reinforced with at least one coated conductive element as defined previously. The elastomeric matrix is based on an elastomeric composition comprising at least one elastomer and another constituent.

Preferably, the elastomeric composition comprises a diene elastomer. An elastomer or rubber (the two terms being synonymous) of the “diene” type generally means an elastomer resulting at least partly (i.e., a homopolymer or a copolymer) from diene monomers (monomers bearing two conjugated or unconjugated carbon-carbon double bonds).

The elastomeric compositions may contain just one diene elastomer or a mixture of several diene elastomers, it being possible for the diene elastomer(s) to be used in combination with any type of synthetic elastomer other than a diene elastomer, or even with polymers other than elastomers, for example thermoplastic polymers.

In a first embodiment preferentially intended for a use in tyres, the elastomeric composition comprises a diene elastomer chosen from the group consisting of polybutadienes (BRs), natural rubber (NR), synthetic polyisoprenes (IRs), the different butadiene copolymers, the different isoprene copolymers and mixtures of these elastomers.

Such copolymers are more preferably chosen from the group consisting of butadiene/styrene copolymers (SBRs), whether the latter are prepared by emulsion polymerization (ESBRs) or solution polymerization (SSBRs), isoprene/butadiene copolymers (BIRs), isoprene/styrene copolymers (SIRs) and isoprene/butadiene/styrene copolymers (SBIRs).

In a second embodiment preferentially intended for use in belts, the elastomeric composition comprises an elastomer chosen from the group consisting of an elastomer of α-olefin ethylene type, a polychloroprene elastomer and mixtures of these elastomers, one or more other elastomers. The elastomeric composition may also comprise one or more other components.

Advantageously, the ethylene/α-olefin type elastomer is chosen from the group consisting of ethylene-propylene copolymers (EPM), ethylene-propylene-diene copolymers (EPDM), and mixtures of these copolymers.

Preferably, the elastomeric composition comprises a reinforcing filler.

When a reinforcing filler is used, use may be made of any type of reinforcing filler known for its abilities to reinforce an elastomeric composition which can be used for the manufacture of tyres, for example an organic filler, such as carbon black, a reinforcing inorganic filler, such as silica, or else a blend of these two types of filler, notably a blend of carbon black and silica.

Any carbon black conventionally used in tyres (“tyre-grade” blacks) is suitable for use as carbon blacks. Mention will more particularly be made, for example, of the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades).

In the case of the use of carbon blacks with an isoprene elastomer, the carbon blacks might, for example, be already incorporated in the isoprene elastomer in the form of a masterbatch (see, for example, patent applications WO 97/36724 or WO 99/16600).

As examples of organic fillers other than carbon blacks, mention may be made of functionalized polyvinylaromatic organic fillers, as described in patent applications WO-A-2006/069792 and WO-A-2006/069793.

The term “reinforcing inorganic filler” should be understood, in the present patent application, by definition, as meaning any inorganic or mineral filler, whatever its colour and its origin (natural or synthetic), also known as “white filler”, “clear filler”, or even “non-black filler”, in contrast to carbon black, which is capable of reinforcing by itself alone, without any means other than an intermediate coupling agent, an elastomeric composition, in other words capable of replacing, in its reinforcing role, a conventional tyre-grade carbon black. Such a filler is generally characterized, in a known manner, by the presence of hydroxyl (—OH) groups at its surface.

The physical state in which the reinforcing inorganic filler is provided is not important, whether it is in the form of a powder, of microbeads, of granules, of beads or any other suitable densified form. Needless to say, the term “reinforcing inorganic filler” also means mixtures of different reinforcing inorganic fillers, in particular of highly dispersible siliceous and/or aluminous fillers as described below.

Mineral fillers of the siliceous type, in particular silica (SiO₂), or of the aluminous type, in particular alumina (Al₂O₃), are notably suitable for use as reinforcing inorganic fillers. The silica used may be any reinforcing silica known to a person skilled in the art, notably any precipitated or fumed silica having a BET surface area and a CTAB specific surface area both of less than 450 m²/g, preferably from 30 to 400 m²/g. Mention will be made, as highly dispersible precipitated silicas (“HDSs”), for example, of the Ultrasil 7000 and Ultrasil 7005 silicas from the company Evonik, the Zeosil 1165MP, 1135MP and 1115MP silicas from the company Rhodia, the Hi-Sil EZ150G silica from the company PPG, the Zeopol 8715, 8745 and 8755 silicas from the company Huber or the silicas with a high specific surface area as described in patent application WO 03/16837.

Finally, a person skilled in the art will understand that, as filler equivalent to the reinforcing inorganic filler described in the present section, use might be made of a reinforcing filler of another nature, notably organic nature, provided that this reinforcing filler is covered with an inorganic layer, such as silica, or else comprises functional sites, in particular hydroxyl sites, on its surface which require the use of a coupling agent in order to establish the bond between the filler and the elastomer.

Preferably, the content of total reinforcing filler (carbon black and/or reinforcing inorganic filler, such as silica) is within a range from 5 to 120 phr, more preferentially from 5 to 100 phr and even more preferentially from 5 to 90 phr.

The carbon black may advantageously constitute the sole reinforcing filler or the predominant reinforcing filler. Needless to say, it is possible to use just one carbon black or a blend of several carbon blacks of different ASTM grades. The carbon black may also be used as a blend with other reinforcing fillers and in particular reinforcing inorganic fillers as described previously, and in particular silica.

When an inorganic filler (for example silica) is used in the rubber composition, alone or as a blend with carbon black, its content is within a range from 0 to 70 phr, preferentially from 0 to 50 phr, in particular also from 5 to 70 phr, and even more preferentially this proportion ranges from 5 to 50 phr, particularly from 5 to 40 phr.

Preferably, the elastomeric composition comprises various additives.

The rubber compositions may also include all or a portion of the usual additives customarily used in elastomeric compositions intended for the manufacture of tyres, for instance plasticizers or extending oils, whether the latter are aromatic or non-aromatic in nature, pigments, protective agents, such as antiozone waxes, chemical antiozonants or antioxidants, antifatigue agents or else adhesion promoters.

Preferably, the elastomeric composition comprises a crosslinking system, more preferentially a vulcanization system.

In the first embodiment preferentially intended for use in tyres, the elastomeric composition comprises a vulcanization system.

The vulcanization system comprises a sulfur-donating agent, for example sulfur.

Preferably, the vulcanization system comprises vulcanization activators, such as zinc oxide and stearic acid.

Preferably, the vulcanization system comprises a vulcanization accelerator and/or a vulcanization retarder.

Advantageously, the composite is such that the elastomeric matrix is based on an elastomeric composition comprising a crosslinking system comprising a content of molecular sulfur ranging from 1 to 5 phr. The term “molecular sulfur” means sulfur resulting from an Sn compound with n>2. Specifically, the inventors put forward the hypothesis that there is competition between adhesion by the adhesive composition and adhesion by the copper and zinc sulfide dendrites. Now, this competition has a tendency to reduce the general level of the adhesion. The more the content of sulfur present in the elastomeric matrix is reduced, the more this competition is reduced, and the more the level of adhesion by the sole adhesive composition is promoted.

Very advantageously, the molecular sulfur content of the crosslinking system of the elastomeric composition is less than or equal to 4 phr, preferably less than or equal to 3 phr and more preferentially less than or equal to 2.5 phr. In addition to further reducing the competition between the adhesion by the adhesive composition and the adhesion by the copper and zinc sulfide dendrites, the shelf life of the elastomeric composition at room temperature is improved, avoiding the risks of prevulcanization which would arise if a higher sulfur content were used.

Very advantageously, the molecular sulfur content of the crosslinking system of the elastomeric composition is greater than or equal to 1.5 phr, preferably greater than or equal to 2 phr.

The sulfur content is measured by elemental analysis, using the Thermo Scientific Flash 2000 microanalyser. The analysis comprises a step of combustion of the sample and then a step of separation of the compounds formed. About 1 mg of sample is introduced into the microanalyser, where it is subjected to flash combustion at 1000° C. under oxygen. The gases formed are then oxidized by virtue of the excess oxygen and of a tungstic anhydride catalyst. A step of reduction by passing over copper subsequently makes it possible to trap the excess oxygen and to reduce the nitrogen oxides to N₂ and also the sulfites to sulfur dioxide SO₂. The water is trapped and the compounds N₂, CO₂ and SO₂ formed are subsequently separated on a chromatographic column and then detected with a katharometer. The total sulfur is quantified by measurement of the area of the SO₂ peak, after calibration with standards.

The combined vulcanization accelerators, retarders and activators are used at a preferential content within a range from 0.5 to 15 phr. The vulcanization activator(s) are used at a preferential content within a range from 0.5 to 12 phr.

The actual crosslinking system is preferentially based on sulfur and on a primary vulcanization accelerator, in particular on an accelerator of the sulfenamide type. Additional to this vulcanization system are various known secondary vulcanization accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), and the like.

Use may be made, as (primary or secondary) accelerator, of any compound that is capable of acting as accelerator for the vulcanization of diene elastomers in the presence of sulfur, notably accelerators of the thiazole type, and also derivatives thereof, and accelerators of thiuram type and of zinc dithiocarbamate type. These accelerators are more preferentially chosen from the group consisting of 2-mercaptobenzothiazole disulfide (abbreviated as “MBTS”), N-cyclohexyl-2-benzothiazolesulfenamide (abbreviated as “CBS”), N,N-dicyclohexyl-2-benzothiazolesulfenamide (abbreviated as “DCBS”), N-(tert-butyl)-2-benzothiazolesulfenamide (abbreviated as “TBBS”), N-(tert-butyl)-2-benzothiazolesulfenimide (abbreviated as “TBSI”), zinc dibenzyldithiocarbamate (abbreviated as “ZBEC”) and mixtures of these compounds. Preferably, use is made of a primary accelerator of the sulfenamide type.

In the second embodiment preferentially intended for use in belts, the crosslinking system is substantially free of sulfur, and advantageously comprises a peroxide, preferably an organic peroxide. Advantageously, the peroxide content ranges from 0.5 to 8 phr. Advantageously, the crosslinking system comprises a co-crosslinking agent, preferably sulfur or triallyl cyanurate. Advantageously, the content of the co-crosslinking agent ranges from 0.5 to 5 phr.

Tyre According to the Invention

The invention also relates to a tyre. The elastomeric composite of the invention may advantageously be used to reinforce tyres for all types of vehicles, in particular passenger vehicles or industrial vehicles, such as heavy-duty vehicles.

Belt According to the Invention

The invention also relates to a belt. For example, such a belt may be a power transmission belt.

USE ACCORDING TO THE INVENTION

The invention also relates to the use of the adhesive composition described previously.

The invention will be better understood on reading the following description, given solely by way of non-limiting example and with reference to the drawings, in which:

FIG. 1 is a diagram of a tyre according to the invention;

FIG. 2 is a diagram of a belt according to the invention;

FIG. 3 is a schematic depiction of an installation for manufacturing a conductive element according to the invention;

FIG. 4 is a diagram of an electroplating device according to the invention of the facility in FIG. 3;

FIG. 5 is a diagram illustrating the various steps of a process for manufacturing a tyre or a belt, an elastomeric composite and a conductive wire element comprising steps of an electroplating process according to the invention;

FIG. 6 is a photograph obtained by scanning electron microscopy of a cross section perpendicular to the main axis of a wire element obtained via a conventional dipping process, and

FIG. 7 is a photograph obtained by scanning electron microscopy of a cross section perpendicular to the main axis of a wire element obtained via the electroplating process according to the invention.

The appended FIG. 1 is a highly diagrammatic representation (without being to a specific scale) of a radial cross section of a tyre in accordance with the invention for a vehicle of the passenger vehicle type.

This tyre 1 includes a crown 2 reinforced by a crown reinforcement or belt 6, two sidewalls 3 and two beads 4, each of these beads 4 being reinforced with a bead wire 5. The crown 2 is surmounted by a tread, not represented in this schematic figure. A carcass reinforcement 7 is wound around the two bead wires 5 in each bead 4, the turn-up 8 of this reinforcement 7 being, for example, positioned towards the outside of the tyre 1, which is represented here fitted onto its wheel rim 9. The carcass reinforcement 7 is, in a manner known per se, formed of at least one ply reinforced with “radial” cords, for example made of textile, that is to say that these cords are positioned virtually parallel to each other and extend from one bead to the other so as to form an angle of between 80° and 90° with the median circumferential plane (plane perpendicular to the axis of rotation of the tyre which is located midway between the two beads 4 and passes through the middle of the crown reinforcement 6).

This tyre 1 of the invention has, for example, the essential feature that at least a crown reinforcement 6 includes a conductive element, in this instance a coated conductive wire element or an elastomeric composite according to the invention. According to another possible exemplary embodiment of the invention, it is, for example, the bead wires which might be entirely or partially composed of a conductive element, in this instance a coated conductive wire element.

FIG. 2 depicts a power transmission belt P. The power transmission belt P is intended for driving any member in rotation. The power transmission belt P comprises an elastomeric body 20 made from an elastomeric matrix and in which coated conductive, in this instance metallic, reinforcing elements R are embedded. The power transmission belt P also comprises a mechanical drive layer 22 arranged in contact with the elastomeric body 20. The mechanical drive layer 22 is provided with several ribs 24 that each extend along a general direction Y substantially perpendicular to a longitudinal direction X of the belt P. Each rib 24 has a trapezoidal shape in cross section. The general directions of the ribs 24 are substantially parallel to each other. The ribs 24 extend over the entire length of the belt P. These ribs 24 are intended to be engaged in recesses or grooves of complementary shape, for example borne by pulleys on which the belt is intended to be mounted.

The elastomeric body 20 is formed on the one hand by a first elastomeric layer 26 made from a first elastomeric matrix and on the other hand by a second elastomeric layer 28 made from a second elastomeric matrix. The mechanical drive layer 22 is formed by a third layer made from a third elastomeric matrix.

Each first and second elastomeric matrix is based, respectively, on a first and second elastomeric composition, each comprising a reinforcing filler, in this instance carbon black (10 to 100 phr), an α, β-unsaturated organic acid metal salt, in this instance zinc monomethacrylate (2 to 50 phr), an agent for dispersing the reinforcing filler (1 to 10 phr), an antioxidant (0.5 to 8 phr), an organic peroxide (0.5 to 8 phr), a co-crosslinking agent (0.5 to 5 phr by weight) and a plasticizer (1 to 20 phr by weight).

At least one of the first and second elastomeric compositions, and thus the elastomeric body 20, also comprises at least one elastomer chosen from the group consisting of an elastomer of α-olefin ethylene type, a polychloroprene (CR) elastomer and mixtures of these elastomers. In the present case, each first and second elastomeric composition comprises a mixture of natural rubber (NR) and of an ethylene-propylene-diene copolymer (EPDM), the proportion of natural rubber being less than 30 phr.

The third elastomeric material based on a third elastomeric composition comprising at least one elastomer chosen from the group consisting of an ethylene/α-olefin type elastomer, a hydrogenated nitrile elastomer (HNBR), a nitrile elastomer (NBR), a chlorosulfonated polyethylene with alkyl groups (ACSM), a polychloroprene elastomer (CR), a polybutadiene (BR), a natural rubber (NR), a synthetic polyisoprene (IR), a butadiene-styrene copolymer (SBR), an isoprene-butadiene copolymer (BIR), an isoprene-styrene copolymer (SIR), a butadiene-styrene-isoprene copolymer (SBIR) and mixtures of these elastomers. In the present case, the elastomer of the elastomeric composition of the third elastomeric matrix is chosen from the group consisting of an ethylene/α-olefin type elastomer, a polychloroprene elastomer (CR), a polybutadiene (BR), a natural rubber (NR), a butadiene-styrene copolymer (SBR) and mixtures of these elastomers. In this instance, the elastomer of the elastomeric composition of the third elastomeric matrix is an ethylene/α-olefin type elastomer, for example an ethylene-propylene copolymer (EPM), an ethylene-propylene-diene copolymer (EPDM) or a mixture of these copolymers.

The belt P according to the invention has, for example, the essential of including several coated conductive elements, in this instance metal wire elements, R and an elastomeric composite 20 according to the invention.

Needless to say, the invention relates to the objects described previously, namely the elastomeric composite and the tyre or belt comprising it, both in the uncured state (before crosslinking) and in the cured state (after crosslinking).

FIG. 3 depicts one embodiment of a facility for manufacturing a conductive wire element according to the invention, denoted by the general reference 30.

The manufacturing facility 30 is suitable for manufacturing conductive wire elements 32 comprising one or more conductive monofilaments. The or each conductive monofilament is advantageously metallic. More preferentially, the or each elementary conductive monofilament comprises a steel core. The steel comprises for example from 0.2% to 1.2%, preferably from 0.3% to 1% and more preferentially from 0.3% to 0.7% of carbon by mass. The steel may also comprise specific alloying elements such as Cr, Ni, Co, V, or various other known elements (see, for example, Research Disclosure 34984—“Micro-alloyed steel cord constructions for tyres”—May 1993; Research Disclosure 34054—“High tensile strength steel cord constructions for tyres”—August 1992). In the present instance, a conventional steel containing 0.7% of carbon is used.

The facility 30 comprises, in the run direction of the conductive wire element 32 in the facility 30, from upstream to downstream, upstream means 34 for storing the conductive wire element 32, a device 36 for electroplating an adhesive composition 38 onto the conductive wire element 32, a device 40 for drying the coated conductive wire element 32, a device 42 for heat-treating the coated conductive wire element 32 and downstream means 44 for storing the heat-treated coated conductive wire element 32.

The upstream 34 and downstream 44 storage means each comprise a reel for storing the conductive wire element 32, making it possible, respectively, to unwind and to wind up the conductive wire element 32.

The electroplating device 36 according to the invention of FIG. 3 is shown in FIG. 4. The electroplating device 36 means 40 for placing the conductive wire element 32 in contact with the adhesive composition 38 and means 42 for creating a potential difference between the adhesive composition 38 and the conductive wire element 32.

The means 40 for placing the conductive wire element 32 in contact with the adhesive composition 38 comprise a tank 45 containing the aqueous adhesive composition 32 and means 46 for continuously passing the conductive wire element 32 through the adhesive composition 38. The throughput means 46 comprise means 48 for unwinding and winding up the conductive wire element 32 which are arranged, respectively, upstream and downstream of the tank 45. Such winding and unwinding means 48 comprise, for example, motorized means for placing in rotation the storage reels of the upstream 34 and downstream 44 storage means.

The means 42 for creating a potential difference between the adhesive composition 38 and the conductive wire element 32 comprise a current generator G, the intensity of which is adjusted as a function of parameters such as the throughput speed of the conductive wire element 32 or the degree of coverage of the conductive wire element 32 with the adhesive composition 38. The means 42 also comprise, on the one hand, electrically conductive pulleys 50, on contact with which the conductive wire element 32 is capable of moving. The pulleys 50 are connected to the current generator G so as to create a potential difference between the electrically conductive pulleys 50 and the adhesive composition 38. In the present instance, the pulleys 50 are connected to the current generator G by means of a contactor 52. The means 42 also comprise an electrode 54 immersed into the adhesive composition 38.

In the embodiment shown, the negative terminal of the current generator G is connected to the adhesive composition and the positive terminal of the current generator G is connected to the conductive wire element 32.

An example of a process for electroplating the adhesive composition 38 onto the conductive wire element 32 will now be described with reference to FIG. 4.

In a first alternative, the conductive wire element 32 comprises only one conductive monofilament.

In a second alternative, the conductive wire element 32 comprises several conductive monofilaments assembled together to form a cable, for example a layered cable or a stranded cable.

During this process, the adhesive composition 38 is electroplated onto the conductive wire element 32.

To do this, the conductive wire element 32 is placed in contact with the adhesive composition 38. In the example described, the adhesive composition 38 comprises water, a mixture of unsaturated elastomer latex, aqueous ammonia and sodium phosphate and a resin based on phloroglucinol and 1,4-benzenedicarboxaldehyde. The proportions of these various constituents are described below. In other embodiments, the resin is based on phloroglucinol and 5-(hydroxymethyl)furfural or based on a precondensed resin based on formaldehyde and resorcinol and 5-(hydroxymethyl)furfural. Other embodiments may also use resins as described previously. The pH of the aqueous adhesive composition ranges from 8 to 14, preferably from 9 to 12 and in this instance is equal to 10.4.

The conductive wire element 32 is immersed in the adhesive composition 38 contained in the tank 44. To do this, the conductive wire element 32 is continuously unwound from the storage reel of the storage means 34 and the conductive wire element 32 is passed through the adhesive composition 38. In the present instance, the conductive wire element 32 is continuously passed through the adhesive composition 38.

A potential difference is applied between the conductive wire element 32 and the adhesive composition 38 so as to coat the conductive wire element with an adhesive layer based on the adhesive composition 38. To do this, the conductive wire element 32 is connected to a potential that is higher than the potential to which the adhesive composition 38 is connected.

Comparative Tests

Corrosion Test

Each conductive wire element comprises a single elementary conductive monofilament, in this instance an elementary metallic monofilament comprising a steel core which has been coated with a metallic layer of brass and which has a diameter equal to 0.32 mm. Each conductive wire element was coated with the test adhesive composition according to a conventional dipping process or an electroplating process according to the invention. Each coated conductive wire element was dried in a drying oven at 180° C. for 30 seconds. The adhesive composition was then crosslinked by passing the coated steel reinforcing elements through a treatment furnace at 240° C. for 30 seconds.

The reinforcing element T0 is a brass-plated steel monofilament free of an adhesive layer.

The reinforcing element T1 is a brass-plated steel monofilament coated with an adhesive layer based on an adhesive composition comprising a resin based on phloroglucinol and 1,4-benzenedicarboxaldehyde deposited by means of a conventional dipping process.

The reinforcing element T2 is a brass-plated steel monofilament coated with an adhesive layer based on an adhesive composition comprising a resin based on phloroglucinol and 1,4-benzenedicarboxaldehyde, the layer being deposited by means of an electroplating process.

The reinforcing element T3 is a brass-plated steel monofilament coated with an adhesive layer based on an adhesive composition comprising Na₃PO₄ and a resin based on phloroglucinol and 1,4-benzenedicarboxaldehyde, the layer being deposited by means of a conventional dipping process.

The reinforcing element E1 is a brass-plated steel monofilament coated with an adhesive layer based on an adhesive composition comprising Na₃PO₄ and a resin based on phloroglucinol and 1,4-benzenedicarboxaldehyde, the layer being deposited by means of an electroplating process.

The reinforcing element E2 is a brass-plated steel monofilament coated with an adhesive layer based on an adhesive composition comprising Na₃PO₄ and a resin based on phloroglucinol and 5-(hydroxymethyl)furfural, the layer being deposited by means of an electroplating process.

The adhesive compositions of the various composites described above are collated in Table 1 below.

TABLE 1 Adhesive compositions T1, T2 T3, E1 E2 Compound A1 1,4-Benzenedicarboxaldehyde (1) 0.89 0.71 — 5-(Hydroxymethyl)furfural (2) — — 1.09 Compound A21/A22 Phloroglucinol (3) 1.67 1.33 1.09 SRF 1524 (4) — — — Sodium hydroxide (5) 0.76 — — Elastomeric latex: NR (6) 6.43 6.43 6.43 SBR (7) 3.24 3.24 3.24 VP-SBR (8) 4.48 4.48 4.48 Aqueous ammonia (9) 0.55 0.55 0.55 Sodium phosphate (10) — 0.75 0.62 Total weight of solids of 19.5 19.5 19.5 adhesive composition Weight of water 80.5 80.5 80.5 (1) 1,4-Benzenedicarboxaldehyde (from the company ABCR; 98% purity); (2) 5-(Hydroxymethyl)furfural (from the company Aldrich; 99% purity); (3) Phloroglucinol (from the company Alfa Aesar; 99% purity); (4) Precondensed resin SRF 1524 (from the company Schenectady; diluted to 75%); (5) Sodium hydroxide (from the company Aldrich; diluted to 30%); (6) NR Latex (“Trang Latex” from the company Bee tex; diluted to 61% by weight); (7) SBR Latex (“Encord-201” from the company Jubilant; diluted to 41% by weight); (8) Vinylpyridine-styrene-butadiene latex (“VP 106S” from the Eliokem; diluted to 41%); (9) Aqueous ammonia (from the company Aldrich; diluted to 21%); (10) Na₃PO₄ sodium phosphate (from the company Aldrich; 99% purity).

The corrosion resistance is characterized by measuring the breaking strength of the coated steel reinforcing elements (denoted as Fmax0) and the breaking strength of the coated steel reinforcing elements after dipping the coated reinforcing element for 4 days in a bath of saline water at 3.5% by mass (denoted Fmax4). The breaking strength Fmax0 is arbitrarily set at 100. The value of the breaking strength Fmax4 of each coated steel reinforcing element is necessarily less than 100, and proportionately all the more so the more sensitive to corrosion the coated reinforcing element.

The decline D, expressed as a percentage, corresponding to the loss of breaking strength between Fmax0 and Fmax4, was calculated. D is such that D=(1−Fmax4−/Fmax0)×100. The lower the decline value D, the lesser the sensitivity of the coated reinforcing element to corrosion.

The results of the tests performed on the coated reinforcing elements are collated in Table 2.

TABLE 2 Coated reinforcing element D (%) T0 33 T1 54 T2 49 T3 51 E1 23 E2 14

It is observed that the coated reinforcing elements E1, E2 according to the invention have a significantly lower decline after corrosion when compared with the control T0.

Comparison of the coated reinforcing elements E1, E2 and T3 shows that the electroplating process is an essential feature of the invention, without which it is not possible to obtain better corrosion resistance.

Comparison of the coated reinforcing elements E1, E2 and T2 shows that the presence of a phosphate salt in the adhesive composition is necessary for improving the corrosion resistance.

Finally, comparison of the reinforcing elements T0 and T1 shows that the resin based on a compound A1 and on a phenol A21 is not sufficient by itself to improve the corrosion resistance.

The invention thus indeed lies in the synergistic combination of the use of an adhesive composition comprising a phosphate salt and a resin as described above in the context of a process for the electroplating of this adhesive composition.

These results also demonstrate particularly efficient corrosion resistance of the coated reinforcing element E2, the decline of which is very low.

Comparison of Scanning Electron Microscope Photographs

Moreover, it is observed, in FIG. 5, which is the scanning electron microscope photograph of a conductive wire element comprising four conductive monofilaments each comprising a steel core coated with an adhesive layer of the adhesive composition used in composite T3 by means of a conventional dipping process, that the deposit of the adhesive layer firstly is not homogeneous, and secondly that this adhesive layer, in places, does not cover the entire outer surface of each conductive monofilament intended to be in contact with the elastomeric matrix.

In contrast, it is observed, in FIG. 6, which is the photograph of a similar wire element coated this time by means of the electroplating process according to the invention, that the deposit of the adhesive layer firstly is homogeneous, and secondly that this adhesive layer covers the entire outer surface of each conductive monofilament intended to be in contact with the elastomeric matrix.

The invention is not limited to the embodiments described previously.

It may also be envisaged to coat several conductive monofilaments each comprising a steel core. In one embodiment, the conductive monofilaments are assembled together and the conductive monofilaments are then collectively coated with the adhesive composition. In another embodiment, each conductive monofilament is individually coated with the adhesive composition and the conductive monofilaments are then assembled together.

Conductive monofilaments coated with a nonmetallic intermediate adhesive layer directly coating the steel core of the conductive monofilaments or the metal coating layer may also be envisaged, the layer of the adhesive composition then directly coating this nonmetallic intermediate adhesive layer or the metal coating layer. 

1.-15. (canceled)
 16. A process for the electroplating of an adhesive composition onto at least one conductive element, the process comprising: placing the conductive element in contact with the adhesive composition, wherein the adhesive composition comprises: at least one phosphate salt, and at least one resin based on: at least one compound A1 selected from the group consisting of: a compound A11 comprising at least two functions, one function being a hydroxymethyl function and one function being an aldehyde function or a hydroxymethyl function, a compound A12 comprising at least one aldehyde function, and a mixture of a compound A11 and of a compound A12, and at least one phenol A21; and applying a potential difference between the conductive element and the adhesive composition so as to coat the conductive element with an adhesive layer based on the adhesive composition.
 17. The process according to claim 16, wherein the conductive element is immersed into the adhesive composition.
 18. The process according to claim 16, wherein the conductive element is passed through the adhesive composition.
 19. The process according to claim 16, wherein the conductive element is connected to a potential that is higher than the potential to which the adhesive composition is connected.
 20. The process according to claim 16, wherein a pH of the aqueous adhesive composition is strictly greater than
 7. 21. The process according to claim 16, wherein the at least one phosphate salt is selected from the group consisting of sodium phosphate, potassium phosphate and mixtures thereof.
 22. The process according to claim 16, wherein the conductive element is a conductive wire element.
 23. The process according to claim 22, wherein the conductive wire element comprises at least one elementary conductive monofilament.
 24. The process according to claim 16, wherein a water content of the adhesive composition is between 70% and 95% by weight.
 25. A device for electroplating an adhesive composition onto at least one conductive element, the device comprising: means for placing the conductive element in contact with the adhesive composition, the adhesive composition comprising: at least one phosphate salt, and at least one resin based on: at least one compound A1 selected from the group consisting of: a compound A11 comprising at least two functions, one function being a hydroxymethyl function and one function being an aldehyde function or a hydroxymethyl function, a compound A12 comprising at least one aldehyde function, and a mixture of a compound All and of a compound A12, and at least one phenol A21; and means for creating a potential difference between the adhesive composition and the conductive element.
 26. The device according to claim 25, wherein the means for creating a potential difference comprise a current generator.
 27. A coated conductive element obtained via the process according to claim
 16. 28. A tire comprising at least one coated conductive element according to claim
 27. 29. A belt comprising at least one coated conductive element according to claim
 27. 